Heat treatment of ferrous sections



May 3, 1938.. P. HOFFMAN El AL 2,116,070

HEAT TREATMENT OF FERROUS SECTIONS Filed Jan. 27, 1936 ATTO R N EYS Patented May 3, lhdd hllhtlt HEAT TREATMENT @F FERRGIUS SECTIONS Paul Hoffman, la Grange,

William Bender,

lDowners (Grove, and Earnshaw lJoolr, Mossmoor, iill., asslgnors, by mesne assignments, to The American ltrahe; Shoe and Foundry @ompany, New hierh, N, 352., a corporation of Delaware application ullarniary 2'7, 119%, Serial No. tutti The invention relates, in general, to the heat treatment of ferrous metal shapes, and more particularly to the quenching at elevated temperatures of selected portions or formed steel shapes, such as the heads of steel rails.

This invention represents an improvement over the method disclosed in copending application Serial No. 3%, filed January 4, 1935, which application discloses a method of heat treating railway track rails of standard specifications and characteristics.

One of the ieatures of the invention consists in subjecting the steel rail or other ferrous metal shape, after heating to a temperature above its critical point, to the quenching action of a bath of molten material, such; as lead or an alloy of lead, that can be maintained at a practically constant desired lower, but elevated temperature, without subjecting other portions or the shape to the direct action of the bath. This treatment promotes theiormation, in both the quenched and unquenched portion of the shape, of distinct grain structure exhibiting desirable relative characteristics in said portions.

Important advantages of the present process as found, for example, in the heat treatment of rails, are to increase the wear-resisting properties of the head and to retain and enhance the toughness and tensile strength of the web and flange. This provides a rail having a traction surface exhibiting higher resistance to wear and a body free of internal stresses and strains to sumciently withstand the stress and shocks. The operation of the process is easily controlled and, after the formed steel shape is heated to the desired initial tfinperature above the critical, the quenching temperature need not be closely maintained, nor need the time, that the submerged portion of the shape is subjected to the molten bath, be closely observed.

The present invention further contemplates the use of a lead pot of limited cross section so that the temperature may be easily controlled. It further contemplates the use of a lead pot having a cross section of such a shape as to provide substantially equal amounts of bath opposite the top face and side faces of the head of the rail.

The invention further contemplates the use of a pot of such shape as to promote the formation of eddy currents therein to assist in equalizing the temperature of the liquid and in extracting the heat from the submerged portion of the formed steel shape.

A further feature of the invention is the provision for reducing the cambering or warping of a claims. (er. rte-21o the rail or, other steel shape. This is accomplish ed by immersing the rail to approximately its neutral axis, and by the use of a layer of coke on the bath to heat insulate the base of the'rail from the bath.

, The invention further consists in the new and novel features of operation and the new and original combination of steps in the process hereinafter described and more particularly set forth in the claims.

Although the novel features which are charac teristic of this invention will he more particularly set forth in the claims appended hereto, the invention itself, as to its objects and advantages and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawing and forming a part thereof, in which Fig. 1 represents a plan view of the bath; and

Fig. 2 represents a cross section through the bath taken on the line i -t of i.

In the following description, the improved process is disclosed particularly with respect to the treatment of railway track rails of standard speciiications and characteristics, but-it will be understood that any' steel shape oi practically any standard specification and many shapes made to particular specifications may be treated. Throughout the specification and in the claims,

the various details will be identified by specific names for convenience, but they are intended to be as generic in their application as the art will commodate the desired length of railway rail 52 1 or other steel shape, and is supported above an elongated furnace it having longitudinally arranged gas or oil burners it and longitudinally arranged air jets it for maintaining the temperature of the bath it at the desired value. These burners it and air jets it are located along hoth sides of the furnace and are arranged to give uniform heating action and uniform cooling action along the length or the furnace.

The bath is provided with suitable elongated supports it, a pair being located at each end, on which the base flange ll of the rail it being treated rests, as indicated. These supports per rnit the head it of the rail to pass into the bath all , (not shown).

Provision is made for close automatic tempera ture regulation. A series of thermocouples 22 are immersed at desired points along the length of the bath. These thermocouples are located preferably at points opposite the side of the rail head It, where it is desired most closely to regulate the a temperature.

Suitable controlling devices (not shown) governed by the thermocouples I! automatically turn on the fuel burners it when the temperature of the bath drops below a certain predetermined value. These devices automatically turn oil the fuel burners it when the temperature of the bath exceeds a certain predetermined value and, at the same time, automatically turn on thecooling Jets iii to bring back the bath to the desired temperature. Likewise, the controlling devices automatically turn on the fuel burners H and turn off the air jets l 5 when the bath temperature falls below a predetermined value.

For removing any lead fumes or other obnoxious gases, a special exhaust system may be provided comprising a series of exhaust boxes, denoted, in general, by 13, connected to a suitable exhaust fan The exhaust boxes are provided with slots 24 and holes 25 for carrying away any obnoxious gases which may be given off during the heat treatment operation. It will be understood that ordinarily, thebath temperatures used for heat treating steel rails are well below the volatilization points of the metals in the bath.

The material of the bath i9 may comprise an alloy of lead and antimony, '9, lead and Y; antimony by weight, having a melting point of about 477 F. These proportions provide a bath which is liquid at 500 E, which temperature has been found to be a desirable quenching temperature for steel rails,

Floating on the surface of the bath may be a layer 20 of coke or other carbonaceous material of, for example, one-half inch in thickness. This material reduces oxidation of the molten bath; prevents the bath from sticking to the rail and heat insulates the bath from the base flange of the rail.

To carry out the improved process, the rail I2 is heated in its entire section in a special heating furnace (not shown) to a temperature above its critical temperature, for example, to about 1500 F. After the rail I2 is thoroughly heated to this temperature, it is immersed in the bath with its head down and with its base flange I'I resting on the supports it, as indicated in Figil. The bath level is arranged so that the rail is immersed to its neutral axis on web 2| which may be about one inch below the bottom of the head for certain weights of rail.

After the rail is submerged in the bath fora sufllcient length of time to give the desired change in structure, the rail may be removed from the bath and subjected as a whole to retarded cooling in air, down to atmospheric temperature,

The particular temperature of the rail prior to quenching is not especially critical so long as it is above the so-called critical temperature, below which no consequential hardening could be effected. In the case of a lb. rail, when the rail is brought to an initial or hardening temperature of 1500 F., it has been found that the temperature drops before quenching to about 1420 F. because of the time nec ssaryfor transporting the rail from the heating furnace to the bath. With heavier rails the drop in temperature will, of course, be correspondingly less.

. The temperature of the bath is not essentially critical, but it has been found that a temperature of 500 1'. gives more desirable characteristics in the quenched and unquenched sections of the rail than the temperatures of 650 to 800 I". disclosed in the former application above referred .to. mth the lower quenching temperature, the head becomes somewhat harder and the other properties of entire rail, are considerably improved.

As disclosed in our earlier application referred to above, the bath temperature should lie preferably above the blue and secondary brittleness ranges, and must lie below the.critical point, or between the limits of, say, 400 1". and 1300' I". It will be noted from the examples given in this and in the earlier application that the preferred operating ranges lie below about 800 F. and above about 400 1''.

When the rail is immersed, the temperature of the lead bath may rise from to 250 F. in spite of the cooling action of the air jets, due to the stored heat in the rail. It may, therefore, be necessary to wait from 10 to 12 minutes after the rail is removed from the bath for the bath to cool on before immersing the next rail. The time for immersion of the rail in the path is not critical, but it has been found that 5 to 10 minutes immersion gives excellent results.

Numerous advantages follow from the above method of heattreatment. Among others, adequate and uniform hardening throughout the quenched areas, including the wearing surfaces on the head, is obtained with a minimum of indueed stresses and without "increasing the hardness of, and yet retaining the toughness of, the

a base and web. The ductility of the base of the rail is actually increased, improving its shockresisting properties and its machinability.

Furthermore, warpa'ge and distortion are practically eliminated. Cambering or bending of the the rail web. The long supports and the exhaust boxes appear to have a lesser effect in eliminating cambering and distortion.

More effective quenching action is obtained by the shape of the lead pot and by the use of relatively small amounts of bath material. When the rail is immersed in the bath material, the higher temperature of the rail causes eddy currents to be set up in the bath which helps maintain the different portions of the bath at uniform temperature and assists in extracting heat from the submerged portion of the rail. The relatively small amount of bath material, which may be as small as 5000 lbs.. assists in providing easier temperature control.

The present process eliminates the hard martensitic carbide transformation in the head, direct transformation from austenite to the fine grained sorbitic pearlite and in the normalized base by direct transformation from austenite to pearlite. Furthermore, the quenching is comran has been reduced by the present invention 2,110,070 pleted at temperatures above the blue brittleness temperature above the critical point, or, if allowed to cool below this point, they may be reheated to the necessary extent in a special furnace provided for this purpose.

If desired, special means may be provided for positively circulating the bath material to accelerate the heat flow from the rail, thereby increasing the quenching rate to obtain greater hardening. For example, an external circulatory system may be provided for withdrawing the molten bath from one end of the container and returning it, after cooling, to the other end of the container.

While certain novel features of the invention have been disclosed and are pointed out'in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. The method 01' heat treating a rail which comprises raising the temperature of the entire rail to above its critical point, immersing the head of the rail in a bath of lead at an elevated temperature while permitting the base flange of the rail to cool in air, and covering said bath with a layer of carbonaceous material to minimize oxidation or the lead, to prevent the lead from sticking to the rail, and to reduce the cam,-

' bering of the rail when it cools.

2. The method oi. heat treating a steel rail -which comprises heating the entire rail to a temperature above the critical point, selectively immersingthe head of the rail in a bath containing molten lead, while permitting the base flange of the rail to cool in air, said bath having a roundcylindrical bottom wall and having a limited cross sectional content so that substantially equal amounts of the bath are disposed at the bottom and sides of the head.

3. The method of selectively heat treating steel railway rails which comprises imparting tothe 5 entire section of the rail a temperature above its upper critical temperature, forthwith selectively immersing for a sustained period of at least five minutes the head of the rail in a lead antimony bath having a temperature range of about 500 to 650 F. while permitting the base flange of the rail to cool in air, cooling the bath and subjecting it to circulation, removing the rail from the bath and cooling the entire rail to atmospheric temperature, thereby to cause the constitution of said head to change from austenite to fine pearlite and the constitution of the unquenched. part of the rail to change from austenite to a pearlite softer than said head, the bath temperature being considerably below the temperature of transformation in the head to offset the mass effect.

4. The method of selectively heat treating steel railway rails which comprises imparting to the entire section of the rail a temperature above its upper critical temperature, immersing the head of the rail in a molten metal bath having a temperature above about 400 F; but below about 800 F., while permitting the base flange of the rail to cool in air, for a time interval sufllcient to cause the constitution of saidhead to change 80 from austenite to fine pearlite and the constitution of the unquenched part of the rail to change from austenite to a pearlite softer than said head, cooling the bath and subjecting it to circulation, removing the rail from the bath and cooling the'entire rail to atmospheric temperature, the bath temperature being considerably below the temperature of transformation in the head to offset the mass efiect.

5. As an article of manufacture, a steel rail- 40 way rail having the composition and hardened by the method substantially as defined in claim 3. 6. As an article of manufacture, a steel'railway rail having the composition and hardened by the method substantially as defined in claim 4.

PAUL HOFFMAN. WILLIAM BEN'DER. EARNSHAW ICOOK. 

